The purpose of this study is to elucidate the pathogenesis of FIV infection in cats starting with the transient primary stage of disease, encompassing the subsequent protracted latent stage of disease, and terminating with the death of animals from AIDS-like disease or other lentivirus-related conditions. The ultimate goal of the research is to demonstrate parallels between HIV infection of man and FIV infection of the cat and, in so doing, to validate FIV infection as a model for the study of human AIDS. The specific aims of the application are studies on the pathogenesis of FIV infection which involve observing the evolution of FIV-induced disease in specific pathogen-free (SPF) cats housed under pathogen-free conditions. Also, the applicant proposes to study co-factors which might accelerate or potentiate FIV-induced disease such as the cattery environment in general and any incidental infectious diseases. The investigator will attempt to define the significance of sero-negative FIV-infected cats (occult carriers?) and to localize viral DNA, RNA, and antigens at various stages of infection and disease. He will also try to define the relationship of naturally- and experimentally-induced FIV infection and cancer and to determine if FIV infection of newborn kittens can serve as a model for pediatric AIDS.